The present invention relates to an image recording apparatus, and in particular, to an image recording apparatus in which image-setting ink is employed.
In recent years, a great number of the image recording apparatuses using ink-jet recording methods have been used. Because the ink-jet recording method can form images very conveniently at low cost, compared to a method in which a plate-making is required, such as a photogravure printing and a flexographic printing.
Further, in the field where images are recorded on commercial products or on their packaging by the ink-jet method, materials such as resin and metal, having no ink absorbing property, are often used for commercial products and their packaging. In order to fix ink drops on a recording medium sheet having no ink absorbing property, image-setting ink is used. Namely, well known is an image recording apparatus using such image-setting ink, wherein after the image-setting ink drops are jetted onto the recording medium sheet, light rays such as ultraviolet light are radiated so that ink drops are hardened and fixed (see Patent Document 1).
In the image recording apparatus, a conveyance unit (which is a conveyance-print device) is disposed which conveys the recording medium sheet, and a plurality of line type printing heads which jet the image-setting ink drops, are arranged above a conveyance path on which the recording medium sheet is fed. Further on the down stream side of the printing heads, with respect to the conveyance direction, a light radiating device is arranged which radiates light rays onto the ink drops jetted from the printing heads, and thereby hardens the ink drops.
In such an image recording apparatus, it is actualized that, while the recording medium sheet is conveyed by the conveyance unit, the ink drops are jetted from the printing heads onto the recording medium sheet, based on predetermined image information, and after which, the light rays from the light radiating device are radiated onto the ink drops, which have landed on the recording medium sheet, and therefore, the ink drops are hardened and fixed on the recording medium sheet.
[Patent Document 1] Tokkai 2002-347232
However, in the image recording apparatus mentioned above, the distance between the light radiating device to each printing head differ. Therefore, the time intervals from an ink drop landed time to a light radiated time also differ for each printing head, resulting in the mixture of the landed color ink and the landed black ink before hardening. Since a text character is generally recorded in black ink, if color or black ink are mixed, specifically when the character is recorded on the recording medium sheet, edges of the black text character become blurred at the area where the black recording overlaps the color recording, resulting in deterioration of text character quality, which is not preferable.